## Description

This adds support for M3 easing and duration tokens.

This PR includes these changes:
* Generation of duration and easing constants, in `Durations` and
`Easing`, respectively (`Curves` is already taken in the `animation`
library)
* Add 3 Dart fixes

Once this is merged, I'll migrate packages/plugins/customers and then
uncomment the deprecation notices for the 3 M2 curves, all of which have
1:1 replacements.

## Related Issues
 - Fixes https://github.com/flutter/flutter/issues/116525

## Tests
 - Added Dart fix tests

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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[test-exempt]:
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[Flutter Style Guide]:
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